Isophorone is an industrial solvent prepared by aldol condensation of acetone. The reaction is carried out in a homogenous media with an alkali hydroxide catalyst or in a heterogeneous media with a mixed oxide catalyst derived from oxides of magnesium and aluminum, or calcium and aluminum. Freshly distilled isophorone has a APHA color of 20-30 as measured by ASTM Standard Test Method for Color of Clear Liquids (Platinum-Cobalt Scale)! but degrades with time to APHA values of 100 or higher. Further it is found that the color deterioration accelerates when the product is stored at elevated temperatures.
Some of the by products made during the synthesis of isophorone have boiling points which are very close to isophorone and therefore are not easily removed by simple distillation. Some of these compounds are responsible for giving the isophorone product a distinct yellow color which may be undesirable.
There are several techniques known in the art to remove color from isophorone. U.S. Pat. No. 2,204,956 discloses a process for purifying ketones. The process includes the addition of ammonia followed by distillation. U.S. Pat. No. 2,968,677 discloses a method of treating colored isophorone with an aromatic sulfonic acid and distilling the isophorone from the mixture. U.S. Pat. No. 4,059,632 discloses the discolorization of isophorone by treatment with phosphoric acid for at least seven hours at 130.degree.-190.degree. C. U.S. Pat. No. 4,248,673 describes a method of treating crude isophorone with acid exchange resins followed by neutralization with excess alkaline reagent and washing to remove the salts formed, and followed by fractionation to purify the isophorone. U.S. Pat. No. 4,434,301 describes a method which comprises contacting crude isophorone with a strong caustic aqueous solution at a temperature of about 140.degree.-200.degree. C. for about for about 1-2 hours, washing the treated isophorone with water and then recovering decolorized isophorone by fractional distillation.
All the above prior art methods require treatment with acidic or basic reagents which necessitate a washing/neutralization stage before the treated isophorone can be distilled. They are also very capital intensive processes which require holding tanks for treatment followed by washing tanks and the need for disposal of the neutralized effluent. Also, all the above methods lead to loss of isophorone yield to products which are not useful.
It is the object of the present invention to produce substantially color free isophorone by a method which is much less capital intensive.
It is also an object of the present invention to produce isophorone which not only has superior color, but superior color stability.